One of the most distinctive features of age-related hearing loss is individual differences. Whereas most studies of individual differences have focused on factors which affect monaural speech recognition, we propose studies of individual differences in both monaural and binaural hearing using psychophysical monaural behavior of older persons focusing on upward spread of masking, frequency discrimination, and forward masking. A related issue involves the prevalence of otoacoustic emissions and other non-linearities which is pertinent to categories of presbyacusis. Aim 1.2 is the assessment of individual differences of older persons in evoked potentials including the auditory brainstem response, steady-state responses, and the N100 -P200. These potentials have been attributed to different neural generators and hypothesized to have different functional significance. Moreover, some age-related declines in frequency and intensity discrimination measured behaviorally may be reflected in steady-state responses. Aim 1.3 is the assessment of individual differences in older persons as indicated by both psychophysical and physiological measurements in complex, binaural experiments. Age-related effects (including individual differences) under these conditions may be magnified, reflecting the effect of an aging periphery auditory system, an aging central nervous system, and the combined effects of the periphery and the central nervous system. That is, small initial changes combine with other small changes throughout the system and produce dramatic changes in the final outcome.. Results of these experiments will provide improvements in the diagnosis, treatment, and management of-related hearing loss as information pertinent to the field of audition.